Polyethylene films

ABSTRACT

A film comprising a polyethylene composition, the polyethylene composition in one embodiment comprising a high molecular weight component having a weight average molecular weight of greater than 50,000 amu and a low molecular weight component having a weight average molecular weight of less than 50,000 amu; the polyethylene composition possessing a density of between 0.940 and 0.970 g/cm 3 , and an I 21  value of less than 20 dg/min; characterized in that the polyethylene composition extrudes at an advantageously high specific throughput at an advantageously low melt temperature, and wherein the film has a gel count of less than 100.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims priority to U.S.Ser. No. 10/781,404, now U.S. Pat. No. 6,878,454, filed Feb. 18, 2004,which claims priority to provisional U.S. Ser. No. 60/527,480, filedDec. 5, 2003, herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to polyethylene films, and moreparticularly, relates to bimodal polyethylene compositions useful infilms having a low level of film impurities and enhanced processability.

BACKGROUND OF THE INVENTION

High density bimodal polyethylene compositions, and in particular, highdensity “bimodal” or “multimodal” polyethylenes (“bHDPE”), are known tobe useful in making films suitable for a variety of commercial productssuch as films, pipes, blow molding, etc. However, the costs of producingsuch compositions is a disadvantage—being relatively high—as most bHDPEsare produced in two stages or more, and/or in two or more stagedreactors such as the processes of Dow, Basell, Borealis and Mitsui. Suchcommercial polymerization systems are reviewed in, for example, 2METALLOCENE-BASED POLYOLEFINS 366–378 (John Scheirs & W. Kaminsky, eds.John Wiley & Sons, Ltd. 2000).

Further, the processing of bHDPEs can present further commercialproblems. For example, it is known that film cooling, upon extrusion ofthe polyethylene, is a limiting factor in film production, especiallyfor extrusion of high density polyethylene, such as described in FILMEXTRUSION MANUAL, PROCESS, MATERIALS, PROPERTIES, pp. 497 (TAPPI, 1992).One solution to this problem is to operate at a desirably low melttemperature. However, given the bimodal nature of these resins, meltingmay be uneven, and/or relatively high melt temperatures must bemaintained for the given resin. To compensate, high back pressures canbe maintained, but this can lead to other problems, and consumes moreenergy. What would be desirable is a bHDPE that can be extruded at arapid rate at a relatively low melt temperature, using lower extrudermotor loads, while maintaining high film quality.

As a further advantage, it would be desirable to use a low cost processto produce bHDPE. Single reactor systems may offer such a costadvantage. While single reactor systems have been described as capableof producing bimodal polyethylenes for film applications, such asdescribed by H.-T Liu et al. in 195 MACROMOL. SYMP. 309–316 (July,2003), those films must still match the quality and processability ofcurrent dual-reactor derived polyethylene films for commercialviability. The present invention in one aspect is directed towards sucha film, as the inventors have found that a certain balance of polymerproperties can meet these commercial needs to produce polyethylene filmssuitable for cast, blown and other film products; and further, that itis possible to achieve these ends using single-reactor producedpolyethylene compositions.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a film comprising apolyethylene composition, preferably a bimodal polyethylene, possessinga density of between 0.940 and 0.970 g/cm³, and an I₂₁ value of lessthan 20 dg/min; characterized in that the polyethylene compositionextrudes at a melt temperature, T^(m), that satisfies the followingrelationship: T^(m)≦235−3.3 (I₂₁); wherein the polyethylene compositionis extruded at a specific throughput of from 1 (0.454 kg/hr/rpm) to 1.5lbs/hr/inch (0.681 kg/hr/rpm), and wherein the film has a gel count ofless than 100.

In another aspect, the present invention provides a film comprising apolyethylene composition, preferably a bimodal polyethylene, thepolyethylene composition comprising a high molecular weight componenthaving a weight average molecular weight of greater than 50,000 amu anda low molecular weight component having a weight average molecularweight of less than 40,000 amu or less than 20,000 amu or less than15,000 amu or less than 12,000 amu; the polyethylene compositionpossessing a density of between 0.940 and 0.970 g/cm³, and an I₂₁ valueof less than 20 dg/min and a Mw/Mn value of from greater than 30 or 35or 40; characterized in that the film has a gel count of less than 100.

In yet another aspect of the invention, the polyethylene compositionsuseful for the films of the invention are produced in a single reactor,preferably a single continuous gas phase reactor.

Various aspects of the present invention can be described by any one, orcombination, of embodiments describing the polymer composition,extrusion properties of the polymer composition, and film, thoseembodiments described in more detail herein.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 and 2 are graphical representations of melt index (I₂₁) valuesof the inventive examples 1 and 2 (♦) and comparative examples (Δ, □)versus motor loads and pressures upon extrusion to form a film of 0.5mil gauge, extruded at a specific throughput of from 1.84 to 1.90lbs/hr/rpm;

FIGS. 3, 4 and 5 are graphical representations of data obtained from GPCcomparing the molecular weight profile of the comparative example 1 (-)with each of inventive examples 3, 4 and 5 (- - - - -); and

FIGS. 6 and 7 are graphical representations of melt index (I₂₁) valuesof the inventive examples 3 and 5 through 9 (♦) and comparative examples(numbered open circles) versus motor loads and pressures upon extrusionto form a film of 0.5 mil gauge, extruded at a specific throughput offrom 1.16 to 1.20 lbs/hr/rpm.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is to a film comprising a polyethylenecomposition, the polyethylene composition in one embodiment comprising ahigh molecular weight component and a low molecular weight componentand, in a particular embodiment, displaying a multimodal or bimodal GPCprofile. The polyethylene composition has improved processing propertiesas exhibited by a decreased extruder motor load (or power consumption)relative to other polyethylene resins of similar density and flow index(I₂₁). Further characteristic of the invention is the high specificthroughput capabilities at advantageously low melt temperatures. Thefilms described herein possess these improved processing propertieswhile maintaining a high film quality, as exemplified by low gelcontent, while maintaining the strength, flexibility and impact strengthcomparable to polyethylenes of similar density and I₂₁.

As used herein, the term “film” or “films” includes skins, sheets, ormembranes of a thickness of from less than 1000 μm, more preferably fromless than 500 μm thickness, and even more preferably less than 200 μm,and most preferably from less than 100 μm, and includes films fabricatedby any process known in the art such as by casting or blowingtechniques—oriented or not—from an extruded or calendered, preferablyextruded, polyethylene as defined herein, and the use of which caninclude any number of functions such as wrapping, protecting, packaging,bagging, coating, co-extrusion with other materials; and further, mayhave any commercially desirable dimensions of width, length, etc. Thefilms of the present invention are not limited to transparent films, andmay be opaque or translucent or transparent, preferably transparent, andhave other properties as defined herein. The films of the presentinvention may be co-extruded with or otherwise secured to othersheets/structures, etc. to form structures of thickness greater than1000 μm.

The benefits inherent in the films of the invention—the requirement oflower motor loads in extruding the polymer compositions to form thefilms, and concomitant with that, the lower melt temperaturesachievable, both while maintaining a commercially acceptable specificthroughput and high film quality as measured by the low gel levelsand/or high FAR values—can be described by any number embodiments suchas described herein.

One aspect of the invention is to a film comprising a polyethylenecomposition possessing a density of between 0.940 and 0.970 g/cm³, andan I₂₁ value of from 4 to 20 dg/min; characterized in that thepolyethylene composition extrudes at a melt temperature, T_(m), thatsatisfies the following relationship (I):T _(m)≦235−3.3(I ₂₁)  (I)wherein the polyethylene composition is extruded at a specificthroughput of from 1 (0.454 kg/hr/rpm) to 1.5 lbs/hr/rpm (0.681kg/hr/rpm), and wherein the film has a gel count of less than 100. Thevalue “I₂₁” is understood to be multiplied by the number “3.3”. Inanother embodiment of (I), the melt temperature is described by therelationship T_(m)≦240−3.3 (I₂₁); and in another embodiment,T_(m)≦240−3.5 (I₂₁); and in yet another embodiment, T_(m)≦235−3.5 (I₂₁).The melt temperature is the temperature at the downstream end of themixing zone of the extruder used in processing the polyethylenecomposition to form the films of the invention. In this aspect of theinvention, the melt temperatures are determined from an extrusion linesuitable to form the film as described herein.

In one embodiment, the polyethylene composition can be described asextruding at a specific throughput of from 1.00 lbs polyethylene/hr/rpm(0.454 kg/hr/rpm) to 1.45 lbs polyethylene/hr/rpm (0.648 kg/hr/rpm) at amelt temperature T_(m) satisfying the equation T_(m)≦235−3.3 (I₂₁).

In another embodiment, the polyethylene composition extrudes at aspecific throughput of from 1.00 lbs polyethylene/hr/rpm (0.454kg/hr/rpm) to 1.40 lbs polyethylene/hr/rpm (0.636 kg/hr/rpm) at a melttemperature T_(m) satisfying the equation T_(m)≦235−3.3 (I₂₁).

In yet another embodiment, the polyethylene composition extrudes at aspecific throughput of from 1.00 lbs polyethylene/hr/rpm (0.454kg/hr/rpm) to 1.30 lbs polyethylene/hr/rpm (0.590 kg/hr/rpm) at a melttemperature T_(m) satisfying the equation T_(m)≦235−3.3 (I₂₁). Inanother embodiment, the lower specific throughput limit is 1.10 lbspolyethylene/hr/rpm (0.499 kg/hr/rpm).

Examples of desirable melt temperatures T_(m) for the polyethylenecompositions of the present invention are values less than 206° C. or204° C. or 202° C. or 200° C. or 198° C. or 196° C. or 190° C. or 188°C. or 186° C. or 184° C. or 182° C. or 180° C. or 179° C., and inanother embodiment, a melt temperature of at least 170° C. or at least175° C. In another embodiment, the lower melt temperature limit is theminimum melt temperature required to obtain films described herein atthe specific throughputs or specific die rates described herein.

In yet another embodiment of the invention, the improved extrusionproperties of the films herein can be described in terms of the specificdie rates; in a particular embodiment, the advantageous die ratesclaimed herein are maintained in a 50 mm grooved feed extruder with anL/D of 21:1 in a particular embodiment. Thus, in one embodiment, thefilm of the invention is formed by extruding the polymer composition ata melt temperature, T_(m), that satisfies the following relationshipT_(m)≦235−3.3 (I₂₁), at a specific die rate of from between 10 and 20pounds of polymer per hour per inch of die circumference (0.179 to 0.357kg/hr/mm), and in another embodiment at a specific die rate of frombetween 10 and 15 pounds of polymer per hour per inch of diecircumference (0.179 to 0.268 kg/hr/mm). In this aspect of theinvention, the melt temperatures are determined from an extrusion linesuitable to form the film as described herein.

In general, the films of the present invention can be described ashaving improved melt temperatures compared to prior art bHDPEs of I₂₁from 4 to 20 dg/min, regardless of the method of its manufacture or themethod of the manufacture of the present polyethylene compositions usedto form the films of the invention. The relationship above in (I) isdefined for a given set of extruder conditions. In one embodiment, thisimprovement is expressed more generally in the relationship T_(m)≦T_(m)^(X)−3.3 (I₂₁), where T_(m) ^(X) is the melt temperature linearextrapolated to the value of I₂₁=0 at any given set of extruderconditions. In general, the melt temperature of the polyethylenecompositions used to make the films of the invention will have valuesfrom 2 to 20° C. lower than that for prior art bHDPEs at the same(within ±2 to ±3 units) of I₂₁.

Another aspect of the invention is to a film comprising a polyethylenecomposition possessing a density of between 0.940 and 0.970 g/cm³, andan I₂₁ value of from 4 to 20 dg/min; characterized in that thepolyethylene composition extrudes at a melt temperature, T_(m), that isfrom 2 or 4 to 10 or 20° C. less than polyethylene compositions ofsimilar density and I₂₁ range produced in a dual or multiple-reactorprocess, and extruded under the same conditions, further characterizedin that the film has a gel count of less than 100. Such dual ormulti-stage and -reactor processes are know in the art such as describedby F. P. Alt et al. in 163 MACROMOL. SYMP. 135–143 (2001) and 2METALLOCENE-BASED POLYOLEFINS 366–378 (2000); and U.S. Pat. No.6,407,185, U.S. Pat. No. 4,975,485 U.S. Pat. No. 4,511,704. As usedherein, the term “multi-reactor polyethylene compositions” refers topolyethylene compositions produced from a staged process comprising theuse of two or more reactors in tandem, or to the use of one reactor thatis operated in a staged manner, as described in those references above.In this aspect of the invention, it is preferable that the melttemperature of the inventive film is compared to the “multi-reactorpolyethylene composition” having an I₂₁ value within ±3 dg/min, morepreferably within ±2 dg/min, and even more preferably within ±1 dg/min.

In yet another aspect of the invention, the film is described ascomprising a polyethylene composition, the polyethylene compositioncomprising a high molecular weight component having a weight averagemolecular weight of greater than 50,000 amu and a low molecular weightcomponent having a weight average molecular weight of less than 40,000amu or less than 20,000 amu or less than 15,000 amu or less than 12,000amu; the polyethylene composition possessing a density of between 0.940and 0.970 g/cm³, and an I₂₁ value of less than 20 dg/min and a Mw/Mnvalue of from greater than 30 or 35 or 40; characterized in that thefilm has a gel count of less than 100. Other characteristics of thepolyethylene composition may be further elucidated as described herein.

The quality of the films of the present invention can be characterizedby the gel count, as described herein. The films have a gel count ofless than 100 in one embodiment, and a gel count of less than 60 inanother embodiment, and a gel count of less than 50 in anotherembodiment, and a gel count of less than 40 in yet another embodiment,and a gel count of less than 35 in yet another embodiment. Describedalternately, the films of the present invention have an FAR value ofgreater than +20 in one embodiment, and greater than +30 in anotherembodiment, and greater than +40 in yet another embodiment. The films ofthe present invention can be formed with a gauge variation of from lessthan 16% of the total thickness in one embodiment, and less than 13% inanother embodiment, and from less than 10% in yet another embodiment.

The polyethylene composition used to make the films of the presentinvention can be extruded at lower power levels and lower pressure, fora given specific throughput and melt temperature, than previously known.For a given extruder, under the same conditions, the polyethylenecompositions of the present invention can be extruded at from 1 to 10%lower motor load relative to comparable bimodal polyethylenecompositions having, the comparison between resins having a density ofbetween 0.940 and 0.970 g/cm³, and an I₂₁ value of less than 20 dg/min.In another embodiment, the improvement is from 2 to 5% lower motor loadrelative to comparable bimodal polyethylene compositions.

Stated another way, for a given extruder, the polyethylene compositionsof the invention having the properties described herein extrude at amotor load of less than 80% the maximum motor load in one embodiment,and less than 77% the maximum motor load in another embodiment, and lessthan 75% the maximum motor load in yet another embodiment, and between66 and 80% maximum motor load in yet another embodiment, and between 70and 77% maximum motor load in yet another embodiment, wherein adesirable range may comprise any combination of any upper % limit withany lower % limit described herein. These advantageous properties existwhile maintaining the melt temperatures and specific throughputsdescribed herein.

The films of the present invention possess properties suitable forcommercial use. For example the films of the invention have an MDTensile strength of from 9,000 to 15,000 psi and a TD Tensile strengthof from 9,000 to 15,000 psi in one embodiment; and an MD Tensileelongation of from 200 to 350% and TD Tensile elongation of from 200 to350% in another embodiment, and an MD Elmendorf Tear value of from 10 to30 g/mil in and a TD Elmendorf Tear value of from 20 to 60 g/mil in yetanother embodiment; and a dart impact (F₅₀) of greater than 150 g in oneembodiment, and greater than 170 g in another embodiment. These valuesare determined under the test methods described further herein.

In one embodiment of the films of the invention, the polyethylenecomposition used to produce the films is preferably free of “hardfoulant” material. These “hard foulants” are zones of inhomogeneousmaterial within the polyethylene composition matrix that have distinctcharacteristics. In one embodiment, the hard gels have a melting point(DSC) of from 125° C. to 133° C., and from 126° C. to 132° C. in anotherembodiment; and further, the hard gels have a I₂₁ of less than 0.5dg/min in one embodiment, and less than 0.4 dg/min in anotherembodiment; and also have an η (0.1 rad/sec at 200° C.) value of fromgreater than 1000 Mpoise in one embodiment, and greater than 1200 Mpoisein another embodiment; wherein the hard gels can be characterized by anyone or combination of these features. By “free of hard foulantmaterial”, it is meant that the hard gels are present, if at all, in anamount no greater than 1 wt % by weight of the total polyethylenecomposition in one embodiment, and less than 0.01 wt % in anotherembodiment, and less than 0.001 wt % in yet another embodiment.

Any desirable method of olefin polymerization—for example, gas phase,slurry phase or solution polymerization process—that is known for thepolymerization of olefins to form polyolefins is suitable for making thepolyethylene composition suitable for the films of the presentinvention. In one embodiment, two or more reactors in series are used,such as, for example, a gas phase and slurry phase reactor in series, ortwo gas phase reactors in series, or two slurry phase reactors inseries. In another embodiment, a single reactor; preferably, a singlegas phase reactor is used. More particularly, this latter embodiment ofthe present invention comprises incorporating a high molecular weight(“HMW”) polyethylene into a low molecular weight (“LMW”) polyethylene,simultaneously in a single reactor, to form the polyethylenecomposition, in the presence of polymerizable monomers and a bimetalliccatalyst composition. The “polyethylene composition” in one embodimentis a bimodal polyethylene composition, wherein from greater than 80 wt%, preferably greater than 90% of the monomer derived units of thecomposition are ethylene and the remaining monomer units are derivedfrom C₃ to C₁₂ olefins and diolefins, described further herein.

In one embodiment, the LMW polyethylene and HMW polyethylene areincorporated into one another either sequentially or simultaneously,preferably simultaneously from one, two or more reactors of any suitabledescription; and are incorporated into one another simultaneously in asingle polymerization reactor in a particular embodiment. In a preferredembodiment of the invention, the polymerization reactor used to make thepolyethylene composition is a fluidized-bed, gas phase reactor such asdisclosed in U.S. Pat. Nos. 4,302,566, 5,834,571, and 5,352,749typically comprising at least one reactor, only one reactor in aparticular embodiment.

In one embodiment, the LMW polyethylene is a polyethylene homopolymer orcopolymer comprising from 0 to 10 wt % C₃ to C₁₀ α-olefin derived units,and more particularly, a homopolymer of ethylene or copolymer ofethylene and 1-butene, 1-pentene or 1-hexene derived units. The LMWpolyethylene can be characterized by a number of factors. The weightaverage molecular weight of the LMW polyethylene ranges from less than50,000 amu in one embodiment, and other embodiments are describedfurther herein.

In one embodiment, the HMW polyethylene is a polyethylene homopolymer orcopolymer comprising from 0 to 10 wt % C₃ to C₁₀ α-olefin derived units,and more particularly, a homopolymer of ethylene or copolymer ofethylene and 1-butene, 1-pentene or 1-hexene derived units. The weightaverage molecular weight of the HMW polyethylene ranges from greaterthan 50,000 amu in one embodiment, and other embodiments as describedfurther herein. The polyethylene composition of the invention,comprising at least the HMW and LMW polymers, can also be described byany number of parameters as described herein.

It is known to use polymerization catalysts in the polymerization ofolefins into polyolefins. The films of the present invention can beproduced by any suitable catalyst composition that provides for theproduction of the polyethylene compositions and films described herein.In one embodiment, the films are produced from polyethylene compositionsproduced from a polymerization process using one class of catalystcompounds, or a combination of two or more of a similar class ofcompounds in another embodiment, or a combination of two or more ofdiffering classes of catalyst compounds in yet another embodiment. In apreferred embodiment, the films comprising the polyethylene compositionsdescribed herein are produced in a polymerization process utilizing abimetallic catalyst composition. Such bimetallic catalyst compositionscomprise at least two, preferably two, Group 3 to Group 10metal-containing compounds, both of which may be the same or differentmetal with similar or differing coordination spheres, patterns ofsubstitution at the metal center or ligands bound to the metal center.Non-limiting examples of suitable olefin polymerization catalysts, whichcan be combined in any number of ways to form a bimetallic catalystcomposition, include metallocenes, Ziegler-Natta catalysts, metal-amidocatalysts as disclosed in, for example, U.S. Pat. Nos. 6,593,438;6,380,328, U.S. Pat. No. 6,274,684, U.S. Pat. No. 6,333,389, WO 99/01460and WO 99/46304; and chromium catalysts such as in U.S. Pat. No.3,324,095, including for example chromium-cyclopentadienyls, chromiumoxides, chromium alkyls, supported and modified variants thereof. Inanother embodiment, the bimetallic catalyst composition is a combinationof two or more of the same class of catalyst compounds.

In a particular embodiment, the bimetallic catalyst composition usefulin making the polymer compositions described herein comprise ametallocene and a titanium-containing Ziegler-Natta catalyst, an exampleof which is disclosed in U.S. Pat. No. 5,539,076, and WO 02/090393, eachincorporated herein by reference. Preferably, the catalyst compounds aresupported, and in a particular embodiment, both catalyst components aresupported with a “primary” activator, alumoxane in a particularembodiment, the support in a particular embodiment being an inorganicoxide support.

In one embodiment, a metallocene catalyst component, as part of thebimetallic catalyst composition, produces the LMW polyethylene of thepolyethylene composition useful for making the films. The metallocenecatalyst compounds as described herein include “full sandwich” compoundshaving two Cp ligands (cyclopentadienyl and ligands isolobal tocyclopentadienyl) bound to at least one Group 3 to Group 12 metal atom,and one or more leaving group(s) bound to the at least one metal atom.Even more particularly, the Cp ligand(s) are selected from the groupconsisting of substituted and unsubstituted cyclopentadienyl ligands andligands isolobal to cyclopentadienyl, non-limiting examples of whichinclude cyclopentadienyl, indenyl, fluorenyl and other structures.Hereinafter, these compounds will be referred to as “metallocenes” or“metallocene catalyst components”.

As used herein, in reference to Periodic Table “Groups” of Elements, the“new” numbering scheme for the Periodic Table Groups are used as in theCRC HANDBOOK OF CHEMISTRY AND PHYSICS (David R. Lide ed., CRC Press81^(st) ed. 2000).

The metal atom “M” of the metallocene catalyst compound is selected fromthe group consisting of Groups 4, 5 and 6 atoms in one embodiment, and aTi, Zr, Hf atoms in yet a more particular embodiment, and Zr in yet amore particular embodiment. The Cp ligand(s) form at least one chemicalbond with the metal atom M to form the “metallocene catalyst compound”.In one aspect of the invention, the metallocene catalyst components ofthe invention are represented by the formula (II):Cp^(A)Cp^(B)MX_(n)  (II)wherein M is as described above; each X is bonded to M; each Cp group ischemically bonded to M; and n is 0 or an integer from 1 to 4, and either1 or 2 in a particular embodiment.

The ligands represented by Cp^(A) and Cp^(B) in formula (II) may be thesame or different cyclopentadienyl ligands or ligands isolobal tocyclopentadienyl, either or both of which may contain heteroatoms andeither or both of which may be substituted by a group R. In oneembodiment, Cp^(A) and Cp^(B) are independently selected from the groupconsisting of cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl,and substituted derivatives of each.

Independently, each Cp^(A) and Cp^(B) of formula (II) may beunsubstituted or substituted with any one or combination of substituentgroups R. Non-limiting examples of substituent groups R as used instructure (II) as well as ring substituents in structure (II) includehydrogen radicals, C₁ to C₆ alkyls, C₂ to C₆ alkenyls, C₃ to C₆cycloalkyls, C₆ to C₁₀ aryls or alkylaryls, and combinations thereof.

Each X in the formula (II) and (III) is independently selected from thegroup consisting of halogen ions (fluoride, chloride, bromide),hydrides, C₁ to C₁₂ alkyls, C₂ to C₁₂ alkenyls, C₆ to C₁₂ aryls, C₇ toC₂₀ alkylaryls, C₁ to C₁₂ alkoxys, C₆ to C₁₆ aryloxys, C₇ to C₁₈alkylaryloxys, C₁ to C₁₂ fluoroalkyls, C₆ to C₁₂ fluoroaryls, and C₁ toC₁₂ heteroatom-containing hydrocarbons and substituted derivativesthereof in a particular embodiment; and fluoride in yet a moreparticular embodiment.

In another aspect of the invention, the metallocene catalyst componentincludes those of formula (I) where Cp^(A) and Cp^(B) are bridged toeach other by at least one bridging group, (A), such that the structureis represented by formula (III):Cp^(A)(A)Cp^(B)MX_(n)  (III)

These bridged compounds represented by formula (III) are known as“bridged metallocenes”. Cp^(A), Cp^(B), M, X and n in structure (III)are as defined above for formula (II); and wherein each Cp ligand isbonded to M, and (A) is chemically bonded to each Cp. Non-limitingexamples of bridging group (A) include divalent hydrocarbon groupscontaining at least one Group 13 to 16 atom, such as but not limited toat least one of a carbon, oxygen, nitrogen, silicon, aluminum, boron,germanium and tin atom and combinations thereof; wherein the heteroatommay also be C₁ to C₁₂ alkyl or aryl substituted to satisfy neutralvalency. The bridging group (A) may also contain substituent groups R asdefined above (for formula (II)) including halogen radicals and iron.More particular non-limiting examples of bridging group (A) arerepresented by C₁ to C₆ alkylenes, substituted C₁ to C₆ alkylenes,oxygen, sulfur, R′₂C═, R′₂Si═, —Si(R′)₂Si(R′₂)—, R′₂Ge═, R′P═ (wherein“═” represents two chemical bonds), where R′ is independently selectedfrom the group consisting of hydride, C₁ to C₁₀ alkyls, aryls andsubstituted aryls.

In one embodiment, a Ziegler-Natta catalyst component, as part of thebimetallic catalyst composition, produces the HMW polyethylene of thepolyethylene composition useful in making the films of the presentinvention. Ziegler-Natta catalyst compounds are disclosed generally inZIEGLER CATALYSTS 363–386 (G. Fink, R. Mulhaupt and H. H. Brintzinger,eds., Springer-Verlag 1995); and RE 33,683. Examples of such catalystsinclude those comprising Group 4, 5 or 6 transition metal oxides,alkoxides and halides, and more particularly oxides, alkoxides andhalide compounds of titanium, zirconium or vanadium in combination witha magnesium compound, internal and/or external electron donors(alcohols, ethers, siloxanes, etc.), aluminum or boron alkyl and alkylhalides, and inorganic oxide supports.

In one embodiment, the Ziegler-Natta catalyst is combined with a supportmaterial, either with or without the metallocene catalyst component. TheZiegler-Natta catalyst component can be combined with, placed on orotherwise affixed to a support in a variety of ways. In one of thoseways, a slurry of the support in a suitable non-polar hydrocarbondiluent is contacted with an organomagnesium compound, which thendissolves in the non-polar hydrocarbon diluent of the slurry to form asolution from which the organomagnesium compound is then deposited ontothe carrier. The organomagnesium compound can be represented by theformula RMgR′, where R′ and R are the same or different C₂–C₁₂ alkylgroups, or C₄–C₁₀ alkyl groups, or C₄–C₈ alkyl groups. In at least onespecific embodiment, the organomagnesium compound is dibutyl magnesium.

The organomagnesium and alcohol-treated slurry is then contacted with atransition metal compound in one embodiment. Suitable transition metalcompounds are compounds of Group 4 and 5 metals that are soluble in thenon-polar hydrocarbon used to form the silica slurry in a particularembodiment. Non-limiting examples of suitable Group 4, 5 or 6 transitionmetal compounds include, for example, titanium and vanadium halides,oxyhalides or alkoxyhalides, such as titanium tetrachloride (TiCl₄),vanadium tetrachloride (VCl₄) and vanadium oxytrichloride (VOCl₃), andtitanium and vanadium alkoxides, wherein the alkoxide moiety has abranched or unbranched alkyl group of 1 to 20 carbon atoms, in aparticular embodiment from 1 to 6 carbon atoms. Mixtures of suchtransition metal compounds may also be used. In a preferred embodiment,TiCl₄ or TiCl₃ is the starting transition metal compound used to formthe magnesium-containing Ziegler-Natta catalyst.

In one embodiment, the Ziegler-Natta catalyst is contacted with anelectron donor, such as tetraethylorthosilicate (TEOS), an ether such astetrahydrofuran, or an organic alcohol having the formula R″OH, where R″is a C₁–C₁₂ alkyl group, or a C₁ to C₈ alkyl group, or a C₂ to C₄ alkylgroup, and/or an ether or cyclic ether such as tetrahydrofuran.

The metallocene and Ziegler-Natta components may be contacted with thesupport in any order. In a particular embodiment of the invention, thefirst catalyst component is reacted first with the support as describedabove, followed by contacting this supported first catalyst componentwith a second catalyst component.

When combined to form the bimetallic catalyst component, the molar ratioof metal from the second catalyst component to the first catalystcomponent (e.g., molar ratio of Ti:Zr) is a value of from 0.1 to 100 inone embodiment; and from 1 to 50 in another embodiment, and from 2 to 20in yet another embodiment, and from 3 to 12 in yet another embodiment;and from 4 to 10 in yet another embodiment, and from 4 to 8 in yetanother embodiment; wherein a desirable molar ratio of Ti componentmetal:Zr catalyst component metal is any combination of any upper limitwith any lower limit described herein.

The polymerization process used to form the polyethylene compositionsuseful in making the films of the invention preferably comprisesinjecting a supported catalyst composition into the polymerizationreactor. The catalyst components and activator(s) (metallocene andZiegler-Natta components) can be combined in any suitable manner withthe support, and supported by any suitable means know in the art.Preferably, the catalyst components are co-supported with at least oneactivator, preferably an alumoxane. Another activator, preferably analkylaluminum, is co-injected into the polymerization reactor as adistinct component in another embodiment. In a most preferredembodiment, the bimetallic catalyst composition, preferably comprising ametallocene and Ziegler-Natta catalyst component, is injected into asingle reactor, preferably a fluidized bed gas phase reactor, underpolymerization conditions suitable for producing a bimodal polyethylenecomposition as described herein.

Supports, methods of supporting, modifying, and activating supports forsingle-site catalyst such as metallocenes is discussed in, for example,by G. G. Hlatky in 100(4) CHEM. REV. 1347–1374 (2000). The terms“support” as used herein refers to any support material, a poroussupport material in one embodiment, including inorganic or organicsupport materials. Particularly preferred support materials includesilica, alumina, silica-alumina, magnesium chloride, graphite, andmixtures thereof in one embodiment. Most preferably, the support issilica. In a particular embodiment, the support is an inorganic oxide,preferably silica, having an average particle size of less than 50 μm orless than 35 μm and a pore volume of from 0.1 to 1 or 2 or 5 cm³/g.

The support is preferably calcined. Suitable calcining temperaturesrange from 500° C. to 1500° C. in one embodiment, and from 600° C. to1200° C. in another embodiment, and from 700° C. to 1000° C. in anotherembodiment, and from 750° C. to 900° C. in yet another embodiment, andfrom 800° C. to 900° C. in yet a more particular embodiment, wherein adesirable range comprises any combination of any upper temperature limitwith any lower temperature limit. Calcining may take place in theabsence of oxygen and moisture by using, for example, an atmosphere ofdry nitrogen. Alternatively, calcining may take place in the presence ofmoisture and air.

The support may be contacted with the other components of the catalystsystem in any number of ways. In one embodiment, the support iscontacted with the activator to form an association between theactivator and support, or a “bound activator”. In another embodiment,the catalyst component may be contacted with the support to form a“bound catalyst component”. In yet another embodiment, the support maybe contacted with the activator and catalyst component together, or witheach partially in any order. The components may be contacted by anysuitable means as in a solution, slurry, or solid form, or somecombination thereof, and may be heated when contacted to from 25° C. to250° C.

In one embodiment, the bimetallic catalyst composition comprises atleast one, preferably one, type of activator. As used herein, the term“activator” is defined to be any compound or combination of compounds,supported or unsupported, which can activate a single-site catalystcompound (e.g., metallocenes, metal amido catalysts, etc.), such as bycreating a cationic species from the catalyst component. Embodiments ofsuch activators include Lewis acids such as cyclic or oligomericpoly(hydrocarbylaluminum oxides). Preferably, the activator is analumoxane, and more preferably, an alumoxane supported on an inorganicoxide support material, wherein the support material has been calcinedprior to contacting with the alumoxane.

An alkylaluminum is also added, preferably to the polymerizationreactor, as an activator of the Ziegler-Natta component of thebimetallic catalyst in one embodiment. The alkylaluminum activator maybe described by the formula AlR^(§) ₃, wherein R^(§) is selected fromthe group consisting of C₁ to C₂₀ alkyls, C₁ to C₂₀ alkoxys, halogen(chlorine, fluorine, bromine) C₆ to C₂₀ aryls, C₇ to C₂₅ alkylaryls, andC₇ to C₂₅ arylalkyls. Non-limiting examples of alkylaluminum compoundsinclude trimethylaluminum, triethylaluminum, triisobutylaluminum,tri-n-hexylaluminum, tri-n-octylaluminum and the like. The alkylaluminumis preferably not supported on the support material with the catalystcomponents and “primary” activator (e.g., alumoxane), but is a separatecomponent added to the reactor(s).

The alkylaluminum compound, or mixture of compounds, such astrimethylaluminum or triethylaluminum is feed into the reactor in oneembodiment at a rate of from 10 wt. ppm to 500 wt. ppm (weight parts permillion alkylaluminum feed rate compared to ethylene feed rate), andfrom 50 wt. ppm to 400 wt. ppm in a more particular embodiment, and from60 wt. ppm to 300 wt. ppm in yet a more particular embodiment, and from80 wt. ppm to 250 wt. ppm in yet a more particular embodiment, and from75 wt. ppm to 150 wt. ppm in yet another embodiment, wherein a desirablerange may comprise any combination of any upper limit with any lowerlimit.

Other primary or separately injected activators known in the art mayalso be useful in making the bimetallic catalyst compositions describedherein. Ionizing activators are well known in the art and are describedby, for example, Eugene You-Xian Chen & Tobin J. Marks, Cocatalysts forMetal-Catalyzed Olefin Polymerization: Activators, Activation Processes,and Structure-Activity Relationships 100(4) CHEMICAL REVIEWS 1391–1434(2000). Illustrative, not limiting examples of ionic ionizing activatorsinclude trialkyl substituted ammonium salts such as triethylammoniumtetra(phenyl)boron and the like; N,N-dialkyl anilinium salts such asN,N-dimethylanilinium tetra(phenyl)boron and the like; dialkyl ammoniumsalts such as di-(isopropyl)ammonium tetra(pentafluorophenyl)boron andthe like; triaryl carbonium salts (trityl salts) such astriphenylcarbonium tetra(phenyl)boron and the like; and triarylphosphonium salts such as triphenylphosphonium tetra(phenyl)boron andthe like, and their aluminum equivalents.

When the activator is a cyclic or oligomeric poly(hydrocarbylaluminumoxide) (i.e., “alumoxane” such as methalumoxane “MAO”), the mole ratioof activator to catalyst component ranges from 2:1 to 100,000:1 in oneembodiment, and from 10:1 to 10,000:1 in another embodiment, and from50:1 to 2,000:1 in yet another embodiment; most preferably, thealumoxane is supported on an inorganic oxide such that, onceco-supported with the metallocene, is present in a molar ratio ofaluminum(alumoxane):Group 4, 5 or 6 metal (metallocene) from 500:1 to10:1, and most preferably a ratio of from 200:1 to 50:1.

Any suitable method (type of polymerization reactor and reactor process,i.e., gas, slurry, solution, high-pressure, etc.) of polymerizingolefins to produce polyethylene having the characteristics as describedherein can be used. The reactor(s) employing the catalyst systemdescribed herein is capable of producing from greater than 500 lbs/hr(230 Kg/hr) in one embodiment, and greater than 1,000 lbs/hr (450 Kg/hr)in another embodiment, and greater than 2,000 lbs/hr (910 Kg/hr) in yetanother embodiment, and greater than 10,000 lbs/hr (4500 Kg/hr) in yetanother embodiment, greater than 20,000 lbs/hr (9,100 Kg/hr) in yetanother embodiment, and up to 500,000 lbs/hr (230,000 Kg/hr) in yetanother embodiment.

Preferably, the films of the present invention are extruded and cast orblown from a polyethylene composition formed from a continuous fluidizedbed gas phase process, and in particular, utilizing a single fluidizedbed reactor in a single stage process. This type of reactor and meansfor operating the reactor are well known and completely described in,for example, U.S. Pat. Nos. 4,003,712, 4,588,790, 4,302,566, 5,834,571,and 5,352,749. Alternately, the process can be carried out in a singlegas phase reactor as described in U.S. Pat. Nos. 5,352,749 and5,462,999. These later patents disclose gas phase polymerizationprocesses wherein the polymerization medium is fluidized by thecontinuous flow of the gaseous monomers and alternately a “condensingagent”.

An embodiment of a fluid bed reactor useful in the process of formingthe polyethylene of the present invention typically comprises a reactionzone and a so-called velocity reduction zone. The reaction zonecomprises a bed of growing polyethylene particles, formed polyethyleneparticles and a minor amount of catalyst particles fluidized by thecontinuous flow of the gaseous monomer and optionally diluent to removeheat of polymerization through the reaction zone. Optionally, some ofthe re-circulated gases may be cooled and compressed to form liquidsthat increase the heat removal capacity of the circulating gas streamwhen readmitted to the reaction zone. A suitable rate of make-up gasflow may be readily determined by simple experiment. Make up of gaseousmonomer to the circulating gas stream is at a rate equal to the rate atwhich particulate polyethylene product and monomer associated therewithis withdrawn from the reactor and the composition of the gas passingthrough the reactor is adjusted to maintain an essentially steady stategaseous composition within the reaction zone. The gas leaving thereaction zone is passed to the velocity reduction zone where entrainedparticles are removed. Finer entrained particles and dust may be removedin a cyclone and/or fine filter. The gas is passed through a recycleline and then through a heat exchanger wherein the heat ofpolymerization is removed, compressed in a compressor and then returnedto the reaction zone. So called “control agents” (e.g., tetrahydrofuran,isopropyl alcohol, molecular oxygen, phenol compounds, ethoxylatedamines, etc) may be added to any part of the reactor system as describedherein, and in a particular embodiment are introduced into the recycleline, preferably at from 0.1 to 50 wt ppm, and in even a more particularembodiment, introduced into the recycle line upstream of the heatexchanger. These agents are known to aid in reduction of electrostaticcharge and/or reactor fouling at the expanded region, recycle line,bottom plate, etc.

In one embodiment, the fluidized bulk density of the polyethylenecomposition forming in the reactor(s) ranges from 16 to 24 lbs/ft³, andfrom 16.5 to 20 lbs/ft³ in another embodiment. The reactor(s) useful inmaking the polyethylene compositions of the present invention preferablyoperate at a space time yield of from 5 to 20 lb/hr/ft³, and morepreferably from 6 to 15 lb/hr/ft³. Further, the residence time in thereactor(s), preferably one reactor, ranges from 1 to 7 hrs, and morepreferably from 1.2 to 6 hrs, and even more preferably from 1.3 to 4hrs.

In the fluidized bed gas-phase reactor embodiment, the reactortemperature of the fluidized bed process herein ranges from 70° C. or75° C. or 80° C. to 90° C. or 95° C. or 100° C. or 110° C., wherein adesirable temperature range comprises any upper temperature limitcombined with any lower temperature limit described herein. In general,the reactor temperature is operated at the highest temperature that isfeasible, taking into account the sintering temperature of thepolyethylene product within the reactor and fouling that may occur inthe reactor or recycle line(s).

In the fluidized bed gas-phase reactor embodiment, the gas phase reactorpressure, wherein gases may comprise hydrogen, ethylene and highercomonomers, and other gases, is between 1 (101 kPa) and 100 atm (10,132kPa) in one embodiment, and between 5 (506 kPa) and 50 atm (5066 kPa) inanother embodiment, and between 10 (1013 kPa) and 40 atm (4050 kPa) inyet another embodiment.

The process of the present invention is suitable for the production ofhomopolymers comprising ethylene derived units, and/or copolymerscomprising ethylene derived units and at least one or more otherolefin(s) derived units. Preferably, ethylene is copolymerized withα-olefins containing from 3 to 12 carbon atoms in one embodiment, andfrom 4 to 10 carbon atoms in yet another embodiment, and from 4 to 8carbon atoms in a preferable embodiment. Even more preferably, ethyleneis copolymerized with 1-butene or 1-hexene, and most preferably,ethylene is copolymerized with 1-butene to form the polyethylenecomposition useful for the films of the invention.

The comonomer may be present at any level that will achieve the desiredweight percent incorporation of the comonomer into the finished resin.In one embodiment of polyethylene production, the comonomer is presentwith ethylene in the circulating gas stream in a mole ratio range offrom 0.005 (comonomer:ethylene) to 0.100, and from 0.0010 to 0.050 inanother embodiment, and from 0.0015 to 0.040 in yet another embodiment,and from 0.018 to 0.035 in yet another embodiment.

Hydrogen gas may also be added to the polymerization reactor(s) tocontrol the final properties (e.g., 12, and/or 12, bulk density) of thepolyethylene composition. In one embodiment, the mole ratio of hydrogento total ethylene monomer (H₂:C₂) in the circulating gas stream is in arange of from 0.001 or 0.002 or 0.003 to 0.014 or 0.016 or 0.018 or0.024, wherein a desirable range may comprise any combination of anyupper mole ratio limit with any lower mole ratio limit described herein.Expressed another way, the amount of hydrogen in the reactor at any timemay range from 1000 ppm to 20,000 ppm in one embodiment, and from 2000to 10,000 in another embodiment, and from 3000 to 8,000 in yet anotherembodiment, and from 4000 to 7000 in yet another embodiment, wherein adesirable range may comprise any upper hydrogen limit with any lowerhydrogen limit described herein.

The bimetallic catalyst composition may be introduced into thepolymerization reactor by any suitable means regardless of the type ofpolymerization reactor used. In one embodiment, the bimetallic catalystcomposition is feed to the reactor in a substantially dry state, meaningthat the isolated solid form of the catalyst has not been diluted orcombined with a diluent prior to entering the reactor. In anotherembodiment, the catalyst composition is combined with a diluent and feedto the reactor; the diluent in one embodiment is an alkane such as a C₄to C₂₀ alkane, toluene, xylene, mineral or silicon oil, or combinationsthereof, such as described in, for example, U.S. Pat. No. 5,290,745.

The bimetallic catalyst composition may be combined with up to 2.5 wt %of a metal-fatty acid compound in one embodiment, such as, for example,an aluminum stearate, based upon the weight of the catalyst system (orits components), such as disclosed in U.S. Pat. No. 6,608,153. Othersuitable metals useful in combination with the fatty acid include otherGroup 2 and Group 5–13 metals. In an alternate embodiment, a solution ofthe metal-fatty acid compound is fed into the reactor. In yet anotherembodiment, the metal-fatty acid compound is mixed with the catalyst andfed into the reactor separately. These agents may be mixed with thecatalyst or may be fed into the reactor in a solution or a slurry withor without the catalyst system or its components.

In another embodiment, the supported catalyst(s) are combined with theactivators and are combined, such as by tumbling and other suitablemeans, with up to 2.5 wt % (by weight of the catalyst composition) of anantistatic agent, such as an ethoxylated or methoxylated amine, anexample of which is Kemamine AS-990 (ICI Specialties, Bloomington Del.).

The polyethylene compositions described herein are multimodal or bimodalin one embodiment, preferably bimodal, and comprise at least one HMWpolyethylene and at least one LMW polyethylene in a particularembodiment. The term “bimodal,” when used to describe the polyethylenecomposition, means “bimodal molecular weight distribution,” which termis understood as having the broadest definition persons in the pertinentart have given that term as reflected in printed publications and issuedpatents. For example, a single polyethylene composition that includespolyolefins with at least one identifiable high molecular weightdistribution and polyolefins with at least one identifiable lowmolecular weight distribution is considered to be a “bimodal”polyolefin, as that term is used herein. Those high and low molecularweight polymers may be identified by deconvolution techniques known inthe art to discern the two polymers from a broad or shouldered GPC curveof the bimodal polyolefins of the invention, and in another embodiment,the GPC curve of the bimodal polymers of the invention may displaydistinct peaks with a trough as shown in the examples in FIGS. 3–5. Thepolyethylene compositions of the invention may be characterized by acombination of features.

In one embodiment, the polyethylene composition is apoly(ethylene-co-1-butene) or a poly(ethylene-co-1-hexene), preferablypoly(ethylene-co-1-butene), the comonomer present from 0.1 to 5 molepercent of the polymer composition, primarily on the LMW polyethylene ofthe polyethylene composition.

The polyethylene compositions of the invention have a density in therange of 0.940 g/cm³ to 0.970 g/cm³ in one embodiment, in the range offrom 0.942 g/cm³ to 0.968 g/cm³ in another embodiment, and in the rangeof from 0.943 g/cm³ to 0.965 g/cm³ in yet another embodiment, and in therange of from 0.944 g/cm³ to 0.962 g/cm³ in yet another embodiment,wherein a desirable density range of the polyethylene compositions ofthe invention comprise any combination of any upper density limit withany lower density limit described herein.

The polyethylene compositions of the present invention can becharacterized by their molecular weight characteristics such as measuredby GPC, described herein. The polyethylene compositions of the inventionhave an number average molecular weight (Mn) value of from 2,000 to70,000 in one embodiment, and from 10,000 to 50,000 in anotherembodiment, and an weight average molecular weight (Mw) of from 50,000to 2,000,000 in one embodiment, and from 70,000 to 1,000,000 in anotherembodiment, and from 80,000 to 800,000 in yet another embodiment. Thebimodal polyolefins of the present invention also have a z-averagemolecular weight (Mz) value ranging from greater than 200,000 in oneembodiment, and from greater than 800,000 in another embodiment, andfrom greater than 900,000 in one embodiment, and from greater than1,000,000 in one embodiment, and greater than 1,100,000 in anotherembodiment, and from greater than 1,200,000 in yet another embodiment,and from less than 1,500,000 in yet another embodiment; wherein adesirable range of Mn, Mw or Mz comprises any combination of any upperlimit with any lower limit as described herein.

The polyethylene compositions of the invention have a molecular weightdistribution, a weight average molecular weight to number averagemolecular weight (M_(w)/M_(n)), or “Polydispersity index”, of fromgreater than 30 or 40 in a preferable embodiment; and a range of from 30to 250 in one embodiment, and from 35 to 220 in another embodiment, andfrom 40 to 200 in yet another embodiment, wherein a desirable embodimentcomprises any combination of any upper limit with any lower limitdescribed herein. The polyethylene compositions also have a “z-average”molecular weight distribution (M_(z)/M_(w)) of from 2 to 20 in oneembodiment, from 3 to 20 in another embodiment, and from 4 to 10 inanother embodiment, and from 5 to 8 in yet another embodiment, and from3 to 10 in yet another embodiment, wherein a desirable range maycomprise any combination of any upper limit with any lower limit.

The polyethylene composition of the present invention possess a meltindex (MI, or I₂ as measured by ASTM-D-1238-E 190° C./2.16 kg) in therange from 0.01 dg/min to 50 dg/min in one embodiment, and from 0.02dg/min to 10 dg/min in another embodiment, and from 0.03 dg/min to 2dg/min in yet another embodiment, wherein a desirable range may compriseany upper limit with any lower limit described herein. The polyethylenecompositions of the invention possess a flow index (FI or I₂₁ asmeasured by ASTM-D-1238-F, 190° C./21.6 kg) ranging from 4 to 20 dg/minin one embodiment, and from 4 to 18 dg/min in another embodiment, andfrom 5 to 16 dg/min in yet another embodiment, and from 6 to 14 dg/minin yet another embodiment; and a range of from 6 to 12 dg/min in yetanother embodiment, wherein a desirable I₂₁ range may comprise any upperlimit with any lower limit described herein. The polyethylenecompositions in certain embodiments have a melt index ratio (I₂₁/I₂) offrom 80 to 400, and from 90 to 300 in another embodiment, and from 100to 250 in yet another embodiment, and from 120 to 220 in yet anotherembodiment, wherein a desirable I₂₁/I₂ range may comprise anycombination of any upper limit with any lower limit described herein.

In another embodiment, the polyethylene compositions comprise greaterthan 50 wt % by weight of the total composition of HMW polyethylene, andgreater than 55 wt % in another embodiment, and in another embodiment,between 50 and 80 wt %, and between 55 and 75 wt % in yet anotherembodiment, and between 55 and 70 wt % in yet another embodiment, theweight percentages determined from GPC measurements.

Further, the polyethylene compositions of the invention possess adynamic viscosity η at 200° C. and 0.1/sec of from 100 kPoise to 3000kPoise in one embodiment, 300 kPoise to 1400 kPoise in anotherembodiment, from 350 kPoise to 1000 kPoise in another embodiment, andfrom 400 kPoise to 800 kPoise in another embodiment, and from 500 kPoiseto 700 kPoise in yet another embodiment. Dynamic viscosity in theexamples herein was measured according to ASTM D4440-95 using a nitrogenatmosphere, 1.5 mm die gap and 25 mm parallel plates at 200° C. and0.1/sec.

In another aspect of the invention, the polyethylene composition usefulfor making the films has an elasticity of greater than 0.60, and greaterthan 0.61 in another embodiment, and greater than 0.62 in yet anotherembodiment, and greater than 0.63 in yet another embodiment.

The individual components of the polyethylene composition may also bedescribed by certain embodiments, and in one embodiment, thepolyethylene composition comprises one HMW polyethylene and one LMWpolyethylene; and in another embodiment, the polyethylene compositionconsists essentially of one HMW polyethylene and one LMW polyethylene.

In one embodiment, the molecular weight distribution (Mw/Mn) of the HMWpolyethylene ranges from 3 to 24, and ranges from 4 to 24 in anotherembodiment, and from 6 to 18 in another embodiment, and from 7 to 16 inanother embodiment, and from 8 to 14 in yet another embodiment, whereina desirable range comprises any combination of any upper limit with anylower limit described herein. The HMW polyethylene has a weight averagemolecular weight ranging from greater than 50,000 amu in one embodiment,and ranging from 50,000 to 1,000,000 amu in one embodiment, and from80,000 to 900,000 amu in another embodiment, and from 100,000 to 800,000amu in another embodiment, and from 250,000 to 700,000 amu in anotherembodiment, wherein a desirable range comprises any combination of anyupper limit with any lower limit described herein. The weight fractionof the HMW polyethylene in the polyethylene composition ranges may be atany desirable level depending on the properties that are desired in thepolyethylene composition; in one embodiment the HMW polyethylene weightfraction ranges from 0.3 to 0.7; and from 0.4 to 0.6 in anotherparticular embodiment, and ranges from 0.5 and 0.6 in yet anotherparticular embodiment.

In one embodiment, the molecular weight distribution (Mw/Mn) of the LMWpolyethylene ranges from 1.8 to 6, and from 2 to 5 in anotherembodiment, and from 2.5 to 4 in yet another embodiment, wherein adesirable range comprises any combination of any upper limit with anylower limit described herein. The LMW polyethylene has a weight averagemolecular weight ranging from 2,000 to 50,000 amu in one embodiment, andfrom 3,000 to 40,000 in another embodiment, and from 4,000 to 30,000 amuin yet another embodiment wherein a desirable range of LMW polyethylenein the polyethylene composition comprises any combination of any upperlimit with any lower limit described herein. In another embodiment, theweight average molecular weight of the LMW polyethylene is less than50,000 amu, and less than 40,000 amu in another embodiment, and lessthan 30,000 amu in yet another embodiment, and less than 20,000 amu inyet another embodiment, and less than 15,000 amu in yet anotherembodiment, and less than 13,000 amu in yet another embodiment. The LMWpolyethylene has an 12 value of from 0.1 to 10,000 dg/min in oneembodiment, and from 1 to 5,000 dg/min in another embodiment, and from100 to 3,000 dg/min in yet another embodiment; and an I₂₁ of from 2.0 to300,000 dg/min in one embodiment, from 20 to 150,000 dg/min in anotherembodiment, and from 30 to 15,000 dg/min in yet another embodiment;wherein for the I₂ and I₂₁ values, a desirable range comprises anycombination of any upper limit with any lower limit described herein.The I₂ and I₂₁ of the LMW polyethylene may be determined by anytechnique known in the art; and in one embodiment is determined bydeconvolution of the GPC curve.

Granules of polyethylene material are formed from the processesdescribed herein in making the polyethylene composition. Optionally, oneor more additives may be blended with the polyethylene composition. Withrespect to the physical process of producing the blend of polyethyleneand one or more additives, sufficient mixing should take place to assurethat a uniform blend will be produced prior to conversion into afinished film product. One method of blending the additives with thepolyolefin is to contact the components in a tumbler or other physicalblending means, the polyolefin being in the form of reactor granules.This can then be followed, if desired, by melt blending in an extruder.Another method of blending the components is to melt blend thepolyolefin pellets with the additives directly in an extruder, Brabenderor any other melt blending means, preferably an extruder. Examples ofsuitable extruders include those made by Farrel and Kobe. While notexpected to influence the measured properties of the polyethylenecompositions described herein, the density, rheological and otherproperties of the polyethylene compositions described in the Examplesare measured after blending additives with the compositions.

Non-limiting examples of additives include processing aids such asfluoroelastomers, polyethylene glycols and polycaprolactones,antioxidants, nucleating agents, acid scavengers, plasticizers,stabilizers, anticorrosion agents, blowing agents, other ultravioletlight absorbers such as chain-breaking antioxidants, etc., quenchers,antistatic agents, slip agents, pigments, dyes and fillers and cureagents such as peroxide.

In particular, antioxidants and stabilizers such as organic phosphites,hindered amines, and phenolic antioxidants may be present in thepolyolefin compositions of the invention from 0.001 to 2 wt % in oneembodiment, and from 0.01 to 1 wt % in another embodiment, and from 0.05to 0.8 wt % in yet another embodiment; described another way, from 1 to5000 ppm by weight of the total polymer composition, and from 100 to3000 ppm in a more particular embodiment. Non-limiting examples oforganic phosphites that are suitable aretris(2,4-di-tert-butylphenyl)phosphite (IRGAFOS 168) anddi(2,4-di-tert-butylphenyl)pentaerithritol diphosphite (ULTRANOX 626).Non-limiting examples of hindered amines includepoly[2-N,N′-di(2,2,6,6-tetramethyl-4-piperidinyl)-hexanediamine-4-(1-amino-1,1,3,3-tetramethylbutane)symtriazine](CHIMASORB 944); bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate (TINUVIN770). Non-limiting examples of phenolic antioxidants includepentaerythrityl tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl) propionate(IRGANOX 1010); 1,3,5-Tri(3,5-di-tert-butyl-4-hydroxybenzyl-isocyanurate(IRGANOX 3114); tris(nonylphenyl)phosphite (TNPP); andOctadecyl-3,5-Di-(tert)-butyl-4-hydroxyhydrocinnamate (IRGANOX 1076);other additives include those such as zinc stearate and zinc oleate.

Fillers may be present from 0.01 to 5 wt % in one embodiment, and from0.1 to 2 wt % of the composition in another embodiment, and from 0.2 to1 wt % in yet another embodiment and most preferably, between 0.02 and0.8 wt %. Desirable fillers include but not limited to titanium dioxide,silicon carbide, silica (and other oxides of silica, precipitated ornot), antimony oxide, lead carbonate, zinc white, lithopone, zircon,corundum, spinel, apatite, Barytes powder, barium sulfate, magnesiter,carbon black, acetylene black, dolomite, calcium carbonate, talc andhydrotalcite compounds of the ions Mg, Ca, or Zn with Al, Cr or Fe andCO₃ and/or HPO₄, hydrated or not; quartz powder, hydrochloric magnesiumcarbonate, glass fibers, clays, alumina, and other metal oxides andcarbonates, metal hydroxides, chrome, phosphorous and brominated flameretardants, antimony trioxide, silica, silicone, and blends thereof.These fillers may particularly include any other fillers and porousfillers and supports known in the art.

In total, fillers, antioxidants and other such additives are preferablypresent to less than 2 wt % in the polyethylene compositions of thepresent invention, preferably less than 1 wt %, and most preferably toless than 0.8 wt % by weight of the total composition.

In one embodiment, an oxidizing agent is also added during thepelletizing step as a reactive component with the polyethylenecomposition. In this aspect of the polyethylene compositions of theinvention, the compositions are extruded with an oxidizing agent,preferably oxygen, as disclosed in WO 03/047839. In one embodiment, from0.01 or 0.1 or 1 to 14 or 16 SCFM (standard cubic feet per minute) ofoxygen is added to the polyethylene composition during extrusion to formthe film, the exact amount depending upon the type of extruder used andother conditions. Stated alternately, from between 10 and 21% by volumeof oxygen in an inert gas such as nitrogen is introduced to theextruding polymer composition in one embodiment. In one embodiment,enough oxygen is added to the extruder to raise the I₂₁/I₂ value of thepolyethylene composition from the reactor(s) by from 1 to 40%, and from5 to 25% in another embodiment. The pellets produced therefrom are thenused to extrude the films of the invention in a separate line, forexample, and Alpine line.

The resultant pelletized polyethylene compositions, with or withoutadditives, are processed by any suitable means for forming films: filmblowing or casting and all methods of film formation to achieve, forexample, uniaxial or biaxial orientation such as described in PLASTICSPROCESSING (Radian Corporation, Noyes Data Corp. 1986). In aparticularly preferred embodiment, the polyethylene compositions of thepresent invention are formed into films such as described in the FILMEXTRUSION MANUAL, PROCESS, MATERIALS, PROPERTIES (TAPPI, 1992). Evenmore particularly, the films of the present invention are blown films,the process for which is described generally in FILM EXTRUSION MANUAL,PROCESS, MATERIALS, PROPERTIES pp. 16–29, for example.

Any extruder suitable for extrusion of a HDPE (density greater than0.940 g/cm³) operating under any desirable conditions for thepolyethylene compositions described herein can be used to produce thefilms of the present invention. Such extruders are known to thoseskilled in the art. Such extruders include those having screw diametersranging from 30 to 150 mm in one embodiment, and from 35 to 120 mm inanother embodiment, and having an output of from 100 to 1,500 lbs/hr inone embodiment, and from 200 to 1,000 lbs/hr in another embodiment. Inone embodiment, a grooved feed extruder is used. The extruder maypossess a L/D ratio of from 80:1 to 2:1 in one embodiment, and from 60:1to 6:1 in another embodiment, and from 40:1 to 12:1 in yet anotherembodiment, and from 30:1 to 16:1 in yet another embodiment.

A mono or multi-layer die can be used. In one embodiment a 50 to 200 mmmonolayer die is used, and a 90 to 160 mm monolayer die in anotherembodiment, and a 100 to 140 mm monolayer die in yet another embodiment,the die having a nominal die gap ranging from 0.6 to 3 mm in oneembodiment, and from 0.8 to 2 mm in another embodiment, and from 1 to1.8 mm in yet another embodiment, wherein a desirable die can bedescribed by any combination of any embodiment described herein. In aparticular embodiment, the advantageous specific throughputs claimedherein are maintained in a 50 mm grooved feed extruder with an L/D of21:1 in a particular embodiment.

The temperature across the zones of the extruder, neck and adapter ofthe extruder ranges from 150° C. to 230° C. in one embodiment, and from160° C. to 210° C. in another embodiment, and from 170° C. to 190° C. inyet another embodiment. The temperature across the die ranges from 160°C. to 250° C. in one embodiment, and from 170° C. to 230° C. in anotherembodiment, and from 180° C. to 210° C. in yet another embodiment.

Thus, the films of the present invention can be described alternately byany of the embodiments disclosed herein, or a combination of any of theembodiments described herein. Embodiments of the invention, while notmeant to be limiting by, may be better understood by reference to thefollowing examples.

EXAMPLES

The following examples relate to gas phase polymerization procedurescarried out in a fluidized bed reactor capable of producing from greaterthan 500 lbs/hr (230 Kg/hr) at a production rate of from 8 to 40 T/hr ormore, utilizing ethylene and 1-butene comonomer, resulting in productionof the polyethylene composition. The tables identify various samples ofresin and films made from those samples, along with the reportedreaction conditions during the collection of the samples (“examples”).Various properties of the resulting resin products and film products arealso identified. Examples 1 and 2 were extruded in the absence of oxygen(“non-tailored”) as described below, while the Examples 3–9 wereextruded in the presence of oxygen (“oxygen tailored”) as per WO03/047839, herein incorporated by reference. The comparative exampleswere made into films as received.

The fluidized bed of the reactor was made up of polyethylene granules.The reactor is passivated with an alkylaluminum, preferablytrimethylaluminum. During each run, the gaseous feed streams of ethyleneand hydrogen were introduced before the reactor bed into a recycle gasline. The injections were downstream of the recycle line heat exchangerand compressor. Liquid 1-butene comonomer was introduced before thereactor bed. The control agent (typically isopropyl alcohol), if any,that influenced resin split and helped control fouling, especiallybottom plate fouling, was added before the reactor bed into a recyclegas line in gaseous or liquid form. The individual flows of ethylene,hydrogen and 1-butene comonomer were controlled to maintain targetreactor conditions, as identified in each example. The concentrations ofgases were measured by an on-line chromatograph.

The examples 1 and 2 were samples taken from a 3–4 day polymerizationrun on a single gas phase fluidized bed reactor having a diameter of 8feet and a bed height (from distributor “bottom” plate to start ofexpanded section) of 38 feet. The examples 3–9 were samples taken from adifferent 3–4 day polymerization run on a single gas phase fluidized bedreactor having a diameter of 11.3 feet and a bed height (fromdistributor “bottom” plate to start of expanded section) of 44.6 feet

In each polymerization run of the inventive examples, supportedbimetallic catalyst was injected directly into the fluidized bed usingpurified nitrogen. Catalyst injection rates were adjusted to maintainapproximately constant production rate. In each run, the catalyst usedwas made with silica dehydrated at 875° C., and metallocene compoundCp₂MX₂ wherein Cp is an n-butyl-substituted cyclopentadienyl ring, M isZirconium; and X is fluoride. The titanium source for the Ziegler-Nattacomponent was TiCl₄.

During each run, the reacting bed of growing polyethylene particles wasmaintained in a fluidized state by a continuous flow of the make-up feedand recycle gas through the reaction zone. As indicated in the tables,each polymerization run for the inventive examples utilized a targetreactor temperature (“Bed Temperature”), namely, a reactor temperatureof about 95° C. During each run, reactor temperature was maintained atan approximately constant level by adjusting up or down the temperatureof the recycle gas to accommodate any changes in the rate of heatgeneration due to the polymerization.

The example polymer compositions were extruded in a 4 inch Farrel (orKobe) Continuous Mixer (4UMSD) at rate of 500 lbs/hr, specific energyinput of 0.125 HP-Hr/lb to form pellets. An additive package was alsoadded such that the Examples 1–9 polymer compositions comprising 800 ppm(IRGANOX 1010,Pentaerythrityltetrakis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-Propionate),200 ppm (IRGAFOS 168, Tris(2,4-di-tert-butyl-phenyl)phosphite) and 1500ppm zinc stearate. The examples 1 and 2 were extruded in a nitrogenatmosphere (0% Oxygen); examples 3–9 were extruded in the presence of anamount of oxygen as disclosed in WO 03/047839.

The polymer composition properties are described in the tables. The“I₂₁:HMW:MFR” is a calculation of the I₂₁ of the high molecular weightcomponent from I₂₁ and I₂ data was based on the following empiricalmodel (IV):

$\begin{matrix}{{{I21}\text{:}{HMW}\text{:}{MFR}} = 2.71828^{{- 0.33759} + {0.516577*\ln\;{I21}} - {0.01523*\frac{I21}{I2}}}} & ({IV})\end{matrix}$where I₂₁ and I₂ were determined from ASTM standards described herein.The “I₂₁:HMW:DSR” is a calculation of the I₂₁ of the high molecularweight component from a dynamic viscosity measurement based on thefollowing model (V):FI:HMW:DSR=η* _(0.1)*2.06694*10⁻⁸−4.40828*ln(G′_(0.1)*1.09839)+5.36175*ln(G″ _(0.1)*1.09275)−0.383985*ln(G″₁₀₀*1.1197)  (V)where

-   -   η*_(x)(Poise) is the complex viscosity determined at 200° C. and        a frequency of x,    -   G′x (dyne/cm²) is the real component of the shear modulus        determined at 200° C. and a frequency of x, and    -   G″x (dyne/cm²) is the imaginary component of the shear modulus        determined at 200° C. and a frequency (rad/sec) of x.

These parameters were measured on a Rheometrics Dynamic StressRheometer, using 25 mm parallel plates, a die gap of approximately 1.4mm, measured, a stress of 10,000 dynes/cm² and the procedure defined inASTM standard D4440-01 Standard Test Method for Plastics: DynamicMechanical Properties: Melt Rheology determinations.

The examples 1 and 2 were extruded blown film line under the conditionslisted in Table 2; the extruder screw being a 50 mm 21 d screw with a“LLDPE” feed section (Alpine part no. 171764). The melt temperatureT_(m) was measured by an immersion thermocouple at the adapter section,near the exit of the extruder. Chilled air was applied to the outside ofthe bubble for cooling purposes.

Other Analytical Methods are Described:

Film gauge was measured according to ASTM D374-94 Method C;

FI (I₂₁): Flow Index (I₂₁) was measured as per ASTM D 1238 at 190° C.,21.6 kg;

MI (I₂): Melt Index (I₂) was measured as per ASTM D 1238 at 190° C.,2.16 kg;

MFR: Melt Flow Ratio is defined as the ratio I₂₁/I₂;

Density (g/cm³): was determined using chips cut from plaques compressionmolded in accordance with ASTM D-4703-00, conditioned in accordance withASTM D618 Procedure A, and measured according to ASTM D1505-03;

Elasticity: This is internal test method and is defined as ratio ofG′/G″ measured at 0.1 radians/second. G′ and G″ are measured on StressRheometer (200° C. using a Dynamic Stree Rheometer) when operating underoscillatory shear at a constant stress of 1000 Pa. The values of G′ andG″ at 0.1 radians/sec is selected for the elasticity number;

η*: Complex viscosity measured on Stress Rheometer at 0.1 radians/sec at200° C.;

FAR: “Film Appearance Rating” is internal test method in which resin isextruded under standard operating guidelines and the resulting film isexamined visually for surface imperfections. The film is compared to areference set of standard film and a FAR rating is assigned based onoperators assessment. This evaluation is conducted by an operator withconsiderable experience. The FAR reference films are available for therange of −50 to +50 and FAR ratings of +20 and better are consideredcommercially acceptable by customers;

Gel count: The equipment used consisted of an Optical Control SystemsGmbH (OCS) Model ME-20 extruder, and OCS Model CR-8 cast film system,and an OCS Model FS-5 gel counter. The ME-20 extruder consists of a ¾″standard screw with 3/1 compression ratio, and 25/1 L/D. It includes afeed zone, a compression zone, and a metering zone. The extruderutilizes all solid state controls, a variable frequency AC drive for thescrew, 5 heating zones including 3 for the barrel, 1 for the melttemperature and pressure measurement zone, and one for the die. The diewas a 4″ fixed lip die of a “fishtail” design, with a die gap of about20 mils. The testing was performed by Southern Analytical, Inc., HoustonTex.

The cast film system includes dual stainless steel chrome plated andpolished chill rolls, a machined precision air knife, rubber nip rollsthat pull the film through the gel counter, and a torque driven wind uproll. The nip rolls are driven separately from the chill rolls and arecontrolled by speed or tension. A circulation cooling/heating system forthe chill rolls was also included, and utilizes ethylene glycol. SteelSS rails, film break sensors, and other items were included. The example3–9 and C1 films that were measured were from 1 mil (25 μm) inthickness, the comparative films C2, C3 and C5 were 2 mil (50 μm) films.

The gel counter consists of a digital 2048 pixel line camera, a halogenbased line lighting system, an image processing computer, and WindowsNT4 software. The camera/light system was mounted on the cast filmsystem between the chill roll and nip rolls, and was set up for a 50micron resolution on film. This means that the smallest defect thatcould be seen was 50 microns by 50 microns in size.

The pellet samples were run with constant extruder temperatures (180° C.for the feed zone, 190° C. for all remaining zones), and constant chillroll temperature of 40° C. The extruder and chill roll speeds werevaried slightly between samples to provide an optimum film for eachsample. With more experimentation, one set of operating conditions mightbe found that are satisfactory for all samples. The gel counter was setup with 10 different size classes beginning at 50–100 microns andincreasing at 100 micron intervals, 4 different shape classes beginningwith a perfect circular shape and increasing to more oblong shapes, andtwo detection levels (one for gels and one for black specks). The geldetection level or sensitivity used was 35 on a 0 to 100 scale.

Once the camera set up parameters were determined, the extruder waspurged with the first sample (typically about 20 minutes) or until itwas apparent that the test conditions were at steady state, or“equilibrium”. This was done by looking at a trend line chart of gelcount number on the “y” axis, and time on the “x” axis. Tests were thenrun on 3 square meters of film per test, as the film moved by thecamera. Three tests were run in succession on the sample, in order todetermine test repeatability. At the end of each 3 square meter test,tabular results were printed. After the purge time, a set of 3successive 3 square meter tests was performed for the second sample, andresults printed.

All gel tests on remaining samples were conducted in this way, exceptthat extruder speed, chill roll speed, and resultant film thickness wasvaried slightly on some samples. Pictures of the actual gels were alsoobtained throughout the testing (in what is called a “mosaic” ofpictures) in order to make sure that what the analyzer was seeing wasreally a gel, and also to make sure that no gel were being measuredtwice or missed. For the granular samples, one set of operatingconditions was found that was adhered to for all samples, including filmthickness, so that all results could be directly comparable.

The gel counts reported in the tables were normalized to gauge. Eachsample was tested three times. The data provided from the test was usedto calculate the sum of all gels 200 microns in size or smaller. Thethree runs from each sample were averaged, then that average divided bythe gauge in mils. The gel count results are normalized as the number ofgels less than 200 μm in size contained in a 3 m² film sample of 1 milthickness, or a volume of 7.62×10⁻⁵ m³.

Dart Impact Strength, F₅₀: Measured on film as per procedure ASTM D1709—Method A;

Elmendorf Tear—Measured on Film as per ASTM D 1922;

1% Secant Modulus: Measured on Film as per ASTM D 882; and

GPC. The Mw/Mn, Mz/Mw, the Mw (weight average molecular weight) and Mn(number average molecular weight) values, and % HMW component, etc. GPCmeasurements were as determined by gel permeation chromatography usingcrosslinked polystyrene columns; pore size sequence: 1 column less than1000, 3 columns of mixed 5×10(7); 1,2,4-trichlorobenzene solvent at 145°C. with refractive index detection. The GPC data was deconvoluted intohigh and low molecular weight components by use of a “Wesslau model”,wherein the β term was restrained for the low molecular weight peak to1.4, as described by E. Broyer & R. F. Abbott, Analysis of molecularweight distribution using multicomponent models, ACS SYMP. SER. (1982),197 (COMPUT. APPL. APPL. POLYM. SCI.), 45–64.

Comparative Example 1 (“C1”) is a single reactor (gas phase) producedbimodal polyethylene having the properties listed in Tables 2 and 4. Itwas made using a bimetallic catalyst system similar to the catalystcomposition described above for the inventive examples.

In order to determine the physical properties of the C1 resin, agranular sample of the C1 was obtained and blended with 1500 ppmTetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane,commonly known as IRGANOX 1010, 1500 ppmTris(2,4-di-t-butylphenyl)phosphite (commonly known as IRGAFOS 168 and1500 ppm zinc stearate. The blended material was melt homogenized undera nitrogen blanket on a laboratory scale Brabender single screwextruder. The FI, MFR and density of the melt homogenized material wasmeasured and is reported in Table 2. Larger amounts of the same C1 wereblended with 200 ppm IRGAFOS 168, 800 ppm IRGANOX 1010 and 1500 ppm zincstearate to determine the film properties. This blend was compounded ona Farrel 18 UMSD at an SEI of 179 kW*H/tonn and 10.2% oxygen at 8.8 SCFMapplied to the melt side of the flow dam. The melt homogenized productof this compounding procedure was converted into film, and the filmprocess and physical properties are reported in Tables 3 and 4. The melttemperatures are the temperature at the downstream end of the mixingzone of the extruder.

Comparative Example 2 (“C2”) is a Dow UNIPOL™ II 2100 bimodalpoly(ethylene-co-1-butene) produced in a two-staged dual reactor gasphase process using a Ziegler-Natta type catalyst.

Comparative Example 3 (“C3”) is a Mitsui HD7960 bimodalpoly(ethylene-co-1-butene) produced in a two-staged slurry process,available from ExxonMobil Chemical Co.

Comparative Example 4 (“C4”) is a Mitsui HD7755 bimodalpoly(ethylene-co-1-butene) produced in a two-staged slurry process,available from ExxonMobil Chemical Co.

Comparative Example 5 (“C5”) is a Alathon™ L5005 bimodalpoly(ethylene-co-1-butene) produced in a two-staged process availablefrom Equistar Chemicals.

TABLE 1 Process Parameters in forming the polyethylene compositionscorresponding to examples 1 and 2, and polymer characteristics 1 2Process Parameter amount of polymer lbs 190,000 230,000 collected in 24hr (±10%) H₂/C₂ Gas Ratio Mol/mol 0.011 0.011 C₄/C₂ Gas Ratio Mol/mol0.026 0.024 C₄/C₂ Flow Ratio Kg/kg 0.0147 0.0152 Ethylene partialpressure Bara 11.3 13.8 Water/C₂ Flow Ratio wt ppm 20.8 20.1 Ti ActivityKg PE/kg 8166 — catalyst TMA in resin wt ppm 113 113 Reactor temperature° C. 95 95 polyethylene composition I₂₁ dg/min 8.5 8.75 I₂₁/I₂ (MFR) 122105 Density g/cc 0.951 0.951 Elasticity 0.57 0.52 η 0.1 s⁻¹/200^(°)C.poise 1,001,000 811,000 I₂₁ HMW dg/min 0.338 0.442 I₂₁ HMW-DSR dg/min0.296 0.381 % HMW-MFR % 54 57 % HMW-DSR % 54 55 % HMW-GPC % 64 65 Mn amu3119 4504 Mw amu 263,733 257,857 Mz amu 1,552,131 1,296,849 Mw/Mn (MWD)84.54 57.24 Mz/Mw 5.89 5.02 LMW-Mw amu 7191 8900 HMW-MW amu 494,890444,430 HMW-MWD 11 9.4

TABLE 2 Film compounding conditions and film properties of comparativeand inventive examples 1 and 2 C4 C1 1 2 Resin Properties I₂₁ dg/min10.6 10.9 8.5 8.75 I₂₁/I₂ 142 111 122 105 Density g/cm³ 0.951 0.9480.951 0.951 Elasticity 0.60 0.52 0.57 0.52 Extruder Conditions ExtruderDiameter mm 50 50 50 50 Extruder L/D 21 21 21 21 Die Diameter mm 120 120120 120 Die Gap mm 1.4 1.4 1.4 1.4 AVG Extruder Set ° C. 190 190 190 190Temp. AVG Die Set Temp. ° C. 200 200 200 200 Stabilizer Yes Yes Yes YesChilled Air Yes Yes Yes Yes Extrusion Properties Rate Lbs/hr 199.7 200.4199.0 199.8 Specific Die Rate Lbs/hr/in 13.5 13.5 13.4 13.5 MeltTemperature ° C. 180.3 184 178.6 178.0 Specific Throughput Lbs/hr/rpm1.90 1.86 1.88 1.84 Motor Load (relative to % 85 87 82 80 maximum forthe instrument) Pressure psi 7370 8065 7676 7415 Film Properties BUR 4 44 4 Gauge mil 0.5 0.5 0.5 0.5 Gauge Variation 16% 13% 27% 22% FAR +50−20 +40 +40/50 Dart Impact Strength F₅₀ g 228 189 174 192 ElmendorfTear - MD g/mil 20 17 19 20 Elmendorf Tear - TD g/mil 31 46 23 37 1%Secant Modulus MD psi 153,000 145,000 186,000 165,000 1% Secant ModulusTD psi 148,000 142,000 154,000 152,000

The examples 1 and 2, produced in a single gas phase reactor using abimetallic catalyst as described, produced polymer compositions havingthe unexpected benefit of improved processability over prior singlereactor bimodal resins and a dual-reactor produced bimodal resincommonly known. The lower power, as also represented in FIGS. 1 and 2,represent a dramatic improvement in film production, as the inventivepolymer compositions can be more easily processed, thus improving itscommercial value. This is especially so given that the I₂₁ values forexamples 1 and 2 are lower than that for both comparative examples, thusthe expectation that the flow through the die to form the film wouldtake more power, not less.

As an even further advantage, the melt temperature of the inventiveexamples 1 and 2 is significantly lower when compared to the comparativeexamples, thus also an improvement in processability. A melt temperatureof less than 180° C., and less than 179° C. in a particular embodiment,is found in the inventive examples, while still maintaining a highspecific die rate of at least 10 lbs polymer/hr/inch of diecircumference and high specific throughput. Thus, if motor loads and/orpressures were applied to the inventive examples 1 and 2 comparable tothe C1 and C4 examples, it is likely that the specific throughputs couldbe at least 1.90 lbs polyethylene/hr/rpm (0.863 kg/hr/rpm) higher atsimilar melt temperatures.

Reactor conditions for runs to produce the polyethylene compositionscorresponding to film examples 3–9 are in Table 3 below. Thepolyethylene composition properties of those corresponding examples arefound in Table 4. Film extrusion conditions for examples 3–9, and fordetermination of the relationship T_(m)≦235−3.3 (I₂₁) and its specificembodiments, are as follows: an Alpine extruder line having a 50 mmgrooved feed extruder, an L/D ratio of 21:1, a temperature profile of180° C. flat across the extruder, and 190° C. flat across the die, 4:1BUR (blow up ratio, the ratio of the initial bubble diameter to the diediameter) an output of 200 lbs/hr, and a 120 mm die with measured 1.4 mmdie gap, using a high-density type screw design; also using single lipair ring (with cooled air) and internal bubble stabilizer; the HDPEscrew being a 50 mm 21 d screw with a HDPE feed section (Alpine part no.116882). The melt temperature T_(m) was measured by an immersionthermocouple at the adapter section, near the exit of the extruder.Examples 3–9 were oxygen tailored similarly to C1. The extrusionproperties and film properties of examples 3–9 are found in Tables 5 and6.

The examples 3–9 exhibited no detectable odor, whereas the C1 sample hassome odor upon extrusion. The examples 3–9, although oxygen tailored andthus exhibiting, on average, larger I₂₁ values and larger I₂ values,still show the improvements of the invention, as these resins are alsomore easily processed relative to the prior art resins.

TABLE 3 Polymerization conditions for Examples 3 through 9 ParameterUnits 3 4 5 6 7 8 9 Amt. PE in 24 hrs Tonnes 156 156 156 156 156 156 156H₂/C₂ mol/mol 0.0085 0.0085 0.009 0.009 0.009 0.009 0.009 C₄/C₂ mol/mol0.0272 0.0272 0.021 0.021 0.021 0.0183 0.0183 C₄/C₂ flow ratio kg/kg0.0166 0.0166 0.0122 0.0122 0.0122 0.0122 0.0122 C₂ partial pressure kPa1400 1400 1400 1400 1400 1400 1400 Ti activity Kg PE/kg 6766 * 5327 59276762 5819 5915 catalyst TMA added to reactor Wt ppm 103 * 96 102 107 101123 Reactor temp ° C. 95 95 95 95 95 95 95 *not recorded, expected to beapproximately the same as other readings

TABLE 4 Polyethylene properties in film examples 3 through 9 andcomparatives density example (g/cm³) I₂₁ (dg/min) I₂₁/I₂ M_(w)/M_(n)elasticity C1 0.950 10.9 123 34 0.62 C2 0.949 10.38 160 26 0.68 C3 0.95211.9 133 — 0.60 C5 0.950 8.6 152 — 0.64 3 0.949 8.39 137 84 0.62 4 0.9499.38 157 83 0.65 5 0.949 11.12 168 90 0.62 6 0.948 8.09 146 82 0.61 70.947 8.61 146 81 0.61 8 0.950 10.01 174 91 0.64 9 0.951 11.5 196 1100.65

TABLE 5 Other polyethylene properties of examples 3 through 9 andcomparatives Property Units 3 4 5 6 7 8 9 C1 C2 C3 C5 Resin PropertiesLMW Mw 7823 8620 8644 8698 8709 7959 6389 16311 21454 — — HMW Mw 444443480543 505190 539136 456299 494016 493254 406641 481868 — — HMW MWD 8.57.3 7.2 7.6 6.5 7.0 12.0 6.3 4.3 — —

TABLE 6 Film properties and extrusion characteristics film examples 3through 9 and comparatives Property Units 3 4 5 6 7 8 9 C1 C2 C3 C5Extrusion Properties Melt Temp ° C. 201 196 195.5 206 204 194 193 206209 200.5 212 Pressure psi 8550 8200 8250 8980 8780 8210 8110 8480 82007960 8450 Motor Load %  77% 71%  74%  78%  77%  75% 74%  82%  82%  77% 80% Specific lbs/hr/ 1.16 1.17 1.18 1.17 1.17 1.18 1.18 1.20 1.18 1.191.19 Throughput rpm Gauge mil 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.50.5 BUR 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 Film Properties FAR40/50 40/50 40/50 40/50 40/50 40/50 50 20 50 50 40 gel count 199 34 3629 32.5 31 28 442 — 218 33 DDI g 182 — 201 178 180 194 — 234 219 270 166MD Tear g/mil 21 — 24 20 22 25 — 21 24 17 22 TD Tear g/mil 30 — 31 32 2731 — 39 41 53 27 MD Tensile psi 11632 — 11389 12324 11156 11140 — 1095912228 11019 11406 Strength TD Tensile psi 11639 — 10942 10404 1227510863 — 10298 12746 11784 10816 Strength MD Tensile % 278% — 288% 251%252% 275% — 295% 299% 408% 279% Elongation TD Tensile % 278% — 273% 304%288% 259% — 297% 322% 356% 385% Elongation MD Yield psi 5840 — 5376 60095786 5374 — 5114 5186 5325 5293 Strength TD Yield psi 4697 — 4575 45484725 4568 — 4652 — 4335 4627 Strength MD Yield %  3% —  4%  5%  5%  5% — 4% —  8%  5% Elongation TD Yield %  6% —  4%  4%  4%  4% —  4% —  5% 6% Elongation

The film quality of examples 3–9 are excellent as indicated by the highFAR values and the low gel counts. Given the equally high FAR values ofexamples 1 and 2, it can be inferred that they too have similarly lowgel counts. Thus, the oxygen tailoring has little to no influence onfilm quality.

Further, the advantages of the films of the present invention can beseen from the data. In particular, at relatively high specificthroughputs, the motor loads, expressed as a percentage of the maximummotor load allowable for the equipment used, are significantly lower—allless than 77 to 78%—for the examples 3 through 9, while that for eachcomparative was typically higher; further, the melt temperatures for theinventive examples were significantly lower than for most of theinventive examples. Also, it can be seen that examples 3–9 follow therelationship T^(m)≦235–3.3 (I₂₁), wherein the polyethylene compositionis extruded at a specific throughput of from 1 to 1.5 lbs/hr/inch, asrepresented graphically at FIG. 6. Further, the more generalrelationship T_(m)≦T_(m) ^(X)−3.3 (I₂₁) is also followed when comparingthe examples 1 and 2, and the examples 3–9, each set having beenextruded under differing conditions and using a different extruderscrews.

More particularly, the advantages of the present invention are evidentby comparing the motor loads (%) and melt temperatures of the inventiveexample 3–9 extrusions versus the comparative examples in Table 5, andgraphically in FIGS. 6 and 7. While the trend for the inventive examplesis towards decreasing melt temperatures and motor loads as I₂₁increases, the comparative resins fall higher for both the extrudermotor load and melt temperature.

It can be seen from the specific throughput, melt temperature and motorload data that the present invention offers a significant improvementover the prior art, even over prior disclosed single reactor bimodalproducts such as disclosed in H. -T Liu et al. in 195 MACROMOL. SYMP.309–316 (July, 2003). The processing parameters of the films in Liu etal—from resins having an I₂₁ of 6.2 dg/min and density of 0.95 g/cm³—arenot as advantageous as the films of the current invention. It should benoted, as see in the FIGS. 3–5 of the present invention, that thebimodal resins of Liu et al. are similar to the C1 above. Certainly, thepresent invention is shown to offer significant improvement over otherprior art bimodal resins having a I₂₁ value of less than 20 and densitywith the range of 0.930 and 0.970 g/cm³, this improvement quitesignificant when taking into account the large commercial quantities ofresin being processed in commercial-scale extruders.

While the present invention has been described and illustrated byreference to particular embodiments, those of ordinary skill in the artwill appreciate that the invention lends itself to many differentvariations not illustrated herein. For these reasons, then, referenceshould be made solely to the appended claims for purposes of determiningthe scope of the present invention. Further, certain features of thepresent invention are described in terms of a set of numerical upperlimits and a set of numerical lower limits. It should be appreciatedthat ranges formed by any combination of these limits are within thescope of the invention unless otherwise indicated.

1. A film comprising a polyethylene composition possessing a density ofbetween 0.944 and 0.962 g/cm³, an I₂₁ value of from 6 to 14 dg/min, anda Mw/Mn value of from greater than 35; characterized in that thepolyethylene composition extrudes at a melt temperature, T_(m), thatsatisfies the following relationship:T _(m)≦235−3.3(I ₂₁) wherein the polyethylene composition is extruded ata specific throughput of from 1.1 to 1.3 lbs/hr/rpm; and wherein thepolyethylene composition formed into a film has a gel count of less than100.
 2. The film of claim 1, wherein the polyethylene compositioncomprises a high molecular weight component having a weight averagemolecular weight of greater than 50,000 amu and a low molecular weightcomponent having a weight average molecular weight of less than 50,000amu.
 3. The film of claim 2, wherein the low molecular weight componentpossesses a weight average molecular weight of less than 40,000 amu. 4.The film of claim 2, wherein the low molecular weight componentpossesses a weight average molecular weight of less than 30,000 amu. 5.The film of claim 1, wherein fillers, antioxidants and other additivesare present to less than 2 wt % in the polyethylene composition.
 6. Thefilm of claim 1, wherein the polyethylene composition has an M_(w)/M_(n)value of from greater than
 40. 7. The film of claim 1, whereinpolyethylene composition has a z-average molecular weight distributionof from 3 to
 20. 8. The film of claim 1, wherein the polyethylenecomposition has an elasticity of greater than 0.60.
 9. The film of claim1, wherein the film has a gel count of less than
 50. 10. The film ofclaim 1, wherein the polyethylene composition is produced in a singlecontinuous gas phase reactor process.
 11. A blown film comprising apolyethylene composition possessing a density of between 0.944 and 0.962g/cm³, an I₂₁ value of from 6 to 14 dg/min, and a Mw/Mn value of fromgreater than 35; characterized in that the polyethylene compositionextrudes at a melt temperature, T_(m), that satisfies the followingrelationship:T _(m)≦240−3.3(I ₂₁) wherein the polyethylene composition is extruded ata specific throughput of from 1.1 to 1.3 lbs/hr/rpm; and wherein thepolyethylene composition formed into a film has a gel count of less than100.
 12. The film of claim 11, wherein the polyethylene compositioncomprises a high molecular weight component having a weight averagemolecular weight of greater than 50,000 amu and a low molecular weightcomponent having a weight average molecular weight of less than 50,000amu.
 13. The film of claim 12, wherein the low molecular weightcomponent possesses a weight average molecular weight of less than40,000 amu.
 14. The film of claim 12, wherein the low molecular weightcomponent possesses a weight average molecular weight of less than30,000 amu.
 15. The film of claim 11, wherein fillers, antioxidants andother additives are present to less than 2 wt % in the polyethylenecomposition.
 16. The film of claim 11, wherein the polyethylenecomposition has an M_(w)/M_(n) value of from greater than
 40. 17. Thefilm of claim 11, wherein polyethylene composition has a z-averagemolecular weight distribution of from 3 to
 20. 18. The film of claim 11,wherein the polyethylene composition has an elasticity of greater than0.60.
 19. The film of claim 11, wherein the film has a gel count of lessthan
 50. 20. The film of claim 1, wherein the polyethylene compositionis produced in a single continuous gas phase reactor process.
 21. Ablown film comprising a polyethylene composition possessing a density ofbetween 0.944 and 0.962 g/cm³, an I₂₁ value of from 6 to 14 dg/min, anda Mw/Mn value of from greater than 35; characterized in that thepolyethylene composition extrudes at a melt temperature, T_(m), thatsatisfies the following relationship:T _(m)≦235−3.5(I ₂₁) wherein the polyethylene composition is extruded ata specific throughput of from 1.1 to 1.3 lbs/hr/rpm; and wherein thepolyethylene composition formed into a film has a gel count of less than100.
 22. The film of claim 21, wherein the polyethylene compositioncomprises a high molecular weight component having a weight averagemolecular weight of greater than 50,000 amu and a low molecular weightcomponent having a weight average molecular weight of less than 50,000amu.
 23. The film of claim 22, wherein the low molecular weightcomponent possesses a weight average molecular weight of less than40,000 amu.
 24. The film of claim 22, wherein the low molecular weightcomponent possesses a weight average molecular weight of less than30,000 amu.
 25. The film of claim 21, wherein fillers, antioxidants andother additives are present to less than 2 wt % in the polyethylenecomposition.
 26. The film of claim 21, wherein the polyethylenecomposition has an M_(w)/M_(n) value of from greater than
 40. 27. Thefilm of claim 21, wherein polyethylene composition has a z-averagemolecular weight distribution of from 3 to
 20. 28. The film of claim 21,wherein the polyethylene composition has an elasticity of greater than0.60.
 29. The film of claim 21, wherein the film has a gel count of lessthan
 50. 30. The film of claim 21, wherein the polyethylene compositionis produced in a single continuous gas phase reactor process.
 31. Ablown film comprising a polyethylene composition possessing a density ofbetween 0.944 and 0.962 g/cm³, an I₂₁ value of from 6 to 14 dg/min, anda Mw/Mn value of from greater than 35; characterized in that thepolyethylene composition extrudes at a melt temperature, T_(m), thatsatisfies the following relationship:T _(m)≦240−3.5(I ₂₁) wherein the polyethylene composition is extruded ata specific throughput of from 1.1 to 1.3 lbs/hr/rpm; and wherein thepolyethylene composition formed into a film has a gel count of less than100.
 32. The film of claim 31, wherein the polyethylene compositioncomprises a high molecular weight component having a weight averagemolecular weight of greater than 50,000 amu and a low molecular weightcomponent having a weight average molecular weight of less than 50,000amu.
 33. The film of claim 32, wherein the low molecular weightcomponent possesses a weight average molecular weight of less than40,000 amu.
 34. The film of claim 32, wherein the low molecular weightcomponent possesses a weight average molecular weight of less than30,000 amu.
 35. The film of claim 31, wherein fillers, antioxidants andother additives are present to less than 2 wt % in the polyethylenecomposition.
 36. The film of claim 31, wherein the polyethylenecomposition has an M_(w)/M_(n) value of from greater than
 40. 37. Thefilm of claim 31, wherein polyethylene composition has a z-averagemolecular weight distribution of from 3 to
 20. 38. The film of claim 31,wherein the polyethylene composition has an elasticity of greater than0.60.
 39. The film of claim 31, wherein the film has a gel count of lessthan
 50. 40. The film of claim 31, wherein the polyethylene compositionis produced in a single continuous gas phase reactor process.